The Effect of Dimpling on the Drag Force of an Automobile in Motion Josh Denzler – Lake Shore High School Mike Oliver – Lake Shore High School

Terminology Drag Force – A force that opposes a projectile’s motion Wake – Area of turbulent air behind a projectile Dimple – A slight depression

Background Gas Prices: Have risen in recent years New Standards: “that will increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by Model Year 2025”

Background Car companies: Making more fuel efficient cars Hybrid technology Lightweight materials Aerodynamics More aerodynamic = less energy to move car Less energy to move car = less fuel consumed

Scientific Concepts Dimpling: Improves aerodynamics of a golf ball Can it improve the aerodynamics of a car?

Previous Research Mythbusters: Zipp: Ran an identical course with dimpled and smooth cars Saw a fuel efficiency increase of three mpg Zipp: Bicycle manufacturer Dimples surface of their disk wheels Better gripping ability on the roads Takes less effort to spin the tire

Previous Research Fastskinz: Dimpled vinyl skin to go over cars Tested by Popular Mechanics: Did not improve fuel efficiency

Problem Do different dimple sizes on a car reduce the drag force acting on that car?

Hypothesis The smooth car, six millimeter dimple, eight millimeter dimple, and ten millimeter dimple will not all have equal drag forces The ten millimeter diameter dimple will result in the largest reduction of drag.

Materials Wind Tunnel Vernier Lab Quest Asus Tablet Lab Car Model

Procedure We are going to insert a video of our procedures here. We will narrate the video appropriately while it is playing.

Sample Data Value Drag Force (N) Smooth Car 6 mm Dimple Car High 0.178 0.230 0.200 0.268 Low .071 0.090 0.012 0.052 Average 0.123 0.140 0.074 0.151

Smooth Car Observations Trial Observation 2 String fell off of pulley, trial redone. 3 Car went back before Lab Quest could get data, trial redone 4 Trials 1-4 were abnormal values and were redone. 6 Abnormally small value, trial redone 11 Abnormal graph of data, data kept 12 13 15 Car did not move, trial redone 16 23, 24 27

6 mm Dimple Car Observations Trial Observation 8 Car did not move, trial redone 12 19

8 mm Dimple Car Observations Trial Observation 8 Second fan not started on time, trial redone 14 Car did not move, trial redone 15 21 22 String fell off of pulley, trial redone. 23

10 mm Dimple Car Observations Trial Observation 2 Car went back before Lab Quest could get data, trial redone 7 String fell off of pulley, trial redone. 8, 10, 12, 15 Car did not move, trial redone 21 Abnormally small value, trial redone 29 30

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Conclusion Purpose: To find out if dimples had an effect on the drag force acting on a car To find which dimple size has the greatest effect on that drag force

Conclusion The Experiment: Used a force sensor Compared drag force acting on different car types Used ANOVA and Two-Sample t Tests Found 8 mm dimple car to have lowest drag force of all car types

Conclusion Initial Hypothesis: The smooth car, six millimeter dimple, eight millimeter dimple, and ten millimeter dimple will not all have equal drag forces The ten millimeter diameter dimple will result in the largest reduction of drag

Conclusion Hypothesis Rejected: Why? All cars did not have same drag force BUT 8 mm car had the lowest drag force Why? A car is not a golf ball Air is not flowing around the car uniformly Design Flaws

Design Flaws Bad Dimpling: Data Not Randomized: Dimples not uniform distance apart Dimples went too far into clay Machine would be more accurate Data Not Randomized: Lurking variables would affect data unevenly Monetary resources Machine could also correct this

Further Research Different Patterns: Other forms of transportation: Different dimples (hexagon, square, etc) Planes Trains Troughs/Ridges Ships Different Car Style: Less sports car like More ball-shaped

Real Life Application Automotive Design: Projectile Design: More fuel efficient cars Decrease oil dependency Help conform to Obama’s standards Projectile Design: Bullets, missiles, balls, etc. Reduces energy needed to fly Can fly further/longer

Any Questions?